Vitamin D status and its relationship with bone mineral density in healthy Asian Indians
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Synthesis of vitamin D takes place in the skin under the effect of sunlight. The Indian subcontinent is situated between 8.4° N and 37.6° N latitudes and has adequate sunshine throughout the year. Thus, it has been presumed that Indians are vitamin D sufficient. We measured serum 25-hydroxy vitamin D [25(OH)D] (n=92) and 1,25-dihydroxy vitamin D [1, 25(OH)2D] (n=65) levels in healthy hospital staff, using 125I radioimmunoassay. Serum intact parathyroid hormone (PTH) concentration was estimated by immunoradiometric assay. Bone mineral density was estimated using a dual energy X-ray absorptiometer (HologicR QDR 4500A). Using a serum 25(OH)D level of 15 ng/ml as a cutoff, 66.3% (61/92) of the subjects were found to be vitamin D deficient. Of these, 20.6% (19/92) subjects had severe vitamin D deficiency (<5 ng/ml), 27.2% (25/92) had moderate vitamin D deficiency (5–9.9 ng/ml), while 18.5% (17/92) had mild vitamin D deficiency (10–14.9 ng/ml). When a serum 25(OH)D level of 20 ng/ml was used as a cutoff, 78.3% subjects were diagnosed to be vitamin D deficient/insufficient. The serum 1,25(OH)2D level was within the normal range (40.6±20.1 pg/ml; mean ± SD). Mean (±SD) serum intact PTH, estimated in a limited number of subjects (n=15), was 72.3 (±21.0) pg/ml (range 36–100 pg/ml). There was a significant correlation between daily sun exposure and 25(OH)D levels (r=0.731, P<0.001). The serum 25(OH)D level correlated with BMD at the femoral neck and Ward's triangle (r=0.50, P=0.020 and r=0.46, P=0.037, respectively). Our findings show that vitamin D deficiency is common in urban north Indian hospital staff. The possible reasons include inadequate sunlight exposure and skin pigmentation in Indians. The serum 1,25(OH)2D level is not a good indicator of vitamin D deficiency. A low serum 25(OH)D level is possibly one of the reasons for lower bone mineral density among Indians.
KeywordsBone mineral density Hypovitaminosis D Serum 1,25-dihydroxy vitamin D Serum 25-hydroxy vitamin D Vitamin D
We sincerely thank all hospital volunteers who cooperated by giving blood samples and undergoing BMD estimation. We acknowledge that without their support the above study would not have been possible. We thank Mr. P. K. Awasthi for help in carrying out assays and Mr. B. R. Verma for helping in BMD estimation. We also thank Miss Jaya Dhaka for secretarial assistance.
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